docs: def ref(self):
          """Get the reference number of the dataset.
  
          Args::
  
            no argument
  
          Returns::
  
            dataset reference number
  
          C library equivalent : SDidtoref
                                                """
  
          sds_ref = _C.SDidtoref(self._id)
          _checkErr('idtoref', sds_ref, 'illegal SDS identifier')
          return sds_ref